Most internal combustion engines, and also some other machines utilizing drive mechanisms, utilize a transmission, in which power is transmitted through a chain or belt. In such a transmission, a movable guide is typically provided in sliding contact with the transmission medium in order to maintain proper tension and to prevent vibration, both in the plane of circulation of the transmission medium and in directions transverse to its plane of circulation. The movable guide is attached to the frame of the engine or other drive mechanism on a mounting shaft consisting of a bolt, a pin, or the like.
FIGS. 11 and 12 show a plastic movable guide G, used in a chain transmission. This guide is described in Japanese laid-open patent publication No. 2002-266964. The guide G comprises a guide body G3 and a plate G5. The guide body G3 is manufactured by integrally molding a shoe G1, adapted for sliding contact with a chain, and a reinforcing structure G2, which extends along the longitudinal direction of the guide. The plate G5 is a steel sheet, which fits into a slot G4 formed between two opposed parts of the reinforcing structure G2, in order to achieve weight reduction while ensuring strength of the guide and rigidity against bending, and in order to facilitate assembly of the guide. In mounting the guide G on a fixed frame, the guide G is attached to the frame by a bolt type pivot shaft B, which extends through mounting hole G6 in the plastic guide G, and through hole G7 in the plate G5.
In the conventional plastic guide, as shown in FIG. 12, the plate G5 is forcibly fitted into the slot G4 so that it is sandwiched between the two opposed parts of the reinforcing structure G2. Thus, the mounting holes G6 and G7, formed respectively in the reinforcing structure G2 and the plate 5, are often initially not in alignment with each other when the combination of the guide body and plate is mounted on the pivot shaft B. In order to align the holes, the plate must be shifted. The needed shift of the plate may be effected by the action of a tapered section formed on the pivot shaft provided that the misalignment does not exceed the distance X depicted in FIG. 12. However, if the holes are too far misaligned, an abutment will take place, preventing the engagement of the guide with the pivot shaft.
When a guide in which the mounting holes G6 and G7 are excessively misaligned is mounted on a frame F, the pivot shaft B abuts a portion of a side of plate G5 adjacent the circumferential edge of the hole G7, and therefore cannot be pushed through the holes G6 and G7. Accordingly, it was necessary to adjust the position of the hole G7 in order to align it with hole G6 and thereby allow the pivot shaft B to be moved through both holes and threaded into to the frame F. The structure depicted in FIGS. 11 and 12, therefore, has the disadvantage that an additional alignment step is required in order to mount the guide on its pivot.
Furthermore, even if the mounting holes G6 and G7 of the guide body and the plate are not excessively misaligned, and the pivot shaft B is forced through the mounting holes, the synthetic resin reinforcing structure G2 tends to break at the location of hole G6, and the difference between strengths of the guide body G3 and the plate G5 produces biased wear of the guide body G3, which impairs the sliding contact function of the guide and also shortens its useful life.
Another problem, with the movable guide of FIGS. 11 and 12, is that, in order to achieve a smooth pivoting action as the guide takes up slack in a chain, it is necessary to supply lubricating oil to the mounting hole G7 in the plate G5. However, maintaining adequate lubrication at the location of mounting hole G7 is difficult.
Accordingly, an object of the invention is to solve the above-described problems of the conventional movable guide, and, more particularly, to provide a movable guide which can be easily and reliably assembled from a synthetic resin guide body and a reinforcing plate, and mounted on the frame of the transmission device. Another object of the invention is to provide a movable guide which can avoid biased wear as it guides a traveling chain or other flexible power transmission medium, and thereby operate reliably over a long period of time.